Off-reel printing presses, whatever the printing process used, print onto a continuous paper web unwinding from a reel. These presses are generally composed of the following components: a reelstand which supplies a paper web at a regulated tension; an infeeder which increases the paper tension provided by the reelstand and which improves the tension regulation; printing units which deposit ink films of various colors onto the paper in so-called "printing" zones; a hot-air drier which dries the ink film by blowing hot air; chill rolls which return the paper to ambient temperature at its exit from the drier; a paper passage which cuts the various webs into strips, superposes them by means of turning bars and puts them in phase so as to bring the pages of the various strips into coincidence by means of cutting registers; and a folder or open-sheet delivery which cuts the continuous web arriving there and, if appropriate, folds it to form a folded booklet.
These various components include a large number of free or driven rollers, on which the running web passes and changes direction. Before the printing press is put into operation, the web has to be "engaged" between or around the various rollers.
The engagement operation has in the past traditionally been carried out by hand. Several operators moving around the machine would pass the leading edge of the paper web to one another. The leading edge of the web may be cut to a point to make it easier to pass it between the many pairs of rollers involved in the printing process.
Manual engagement of the web is lengthy and laborious, because it is necessary to climb into the structure of the machine in order to engage the web on the paperpassage rollers, and could be dangerous if the various pairs of engaging rollers were not protected by "finger guards".
It should also be noted that, on most printing presses, the paper does not follow a single path. Depending on the final product desired, it can follow different paper paths and therefore pass over the various rollers in a different order.
An improved engagement system known as "engagement belts" is well known. This system involves providing idle pulleys at the end of the various rollers on which an endless belts travels following the path most often travelled by the paper. When it has reached the end of its travel, this belt has to return to its starting point on a series of so-called return pulleys. It is necessary to provide tensioning devices for keeping this belt at a suitable tension and a drive device for driving the system as a whole. To engage the paper, it is cut obliquely to make a point, on the side where the engagement belts is located, this point is attached to the engagement belts and the press and the drive system of the cords are put into operation so that the paper is carried by these from roller to roller. It should be noted, however, that such belts have single and invariable paths and therefore do not allow a plurality of paper passes to be executed according to choice. This system is generally satisfactory, especially on presses for printing the daily newspapers.
This system can be modified to provide a plurality of belts, for example one on each side of the breadth of the paper to be engaged, these belts carrying out the engagement along different paths. In this arrangement, moreover, the paper can be secured to one of the belts over a particular length of the path and to the other belts over another part. It should be noted, however, that this solution is not fully automatic and requires a considerable involvement of personnel.
There are other known engagement systems, in which a bar passes across the width of the paper breadth, being connected on the two sides of the latter to chains or to cables driven in synchronism by a winch located at the end of the machine. In this arrangement, the chains or cables pass over pulleys, the axles of which are fastened on either side of the frames of the machine. To engage the web, its end is fastened to the engagement bar by means of adhesive tape and the printing press and winch are set in slow motion. The engagement bar is displaced according to the path of the chains or cables and introduces the web along this path. This system can be "endless" with the chains or cables arranged on a continuous looped path.
Other systems employ an unwinder having an "unwinding" chain or cable winch and a "winding" winch near the folder end of the machine. When the web has been engaged, the bar of the chain or cable drive system is disconnected and the chain or cable is rewound onto the "unwinding" winch. Here again, the main disadvantage of this system is that it enables the paper to be engaged only along a single path.
Systems have been proposed, in which a roller chain section of a length of only a few meters is displaced in a channel fastened against the frame of the machine. This channel has a C-shaped cross-section, thus ensuring that the chain is retained in the channel. At the rear of the chain section, a hook emerges through the orifice of the channel and serves for attaching the point formed in the paper web to be engaged. Of course, the chain is arranged in the channel in such a way that its rollers and therefore its axes of articulation are parallel to the axes of the rollers and cylinders of the press. To drive this chain, along the channel, there are at a fixed station electric or pneumatic motors driving chain pinions, the axes of which are themselves parallel to the axes of the rollers of the press. These chain pinions mesh with the chain through slots made at fixed intervals in the wall of the chain guide channel.
The roller chain arrangement is such that the distance, along the channel, between two chain pinions is smaller than the length of the chain section, so that this section is pushed along in the channel as far as the following pinion which then meshes with it and pulls it. Electric or pneumatic chain presence detectors are used for starting and stopping the motors, these operating only when a chain passes through them.
The advantage of this system over the preceding ones is that it makes it possible to engage the web along varied paths. It is possible, in fact, to arrange switches on the channels between the various sections and to direct the chain different ways.